To rotate the view of the page shown on-screen, select Rotate pages from the View menu and choose an option from the sub-menu
|Clockwise (90 degrees right)
|Anticlockwise (90 degrees left)
|Upsidedown (180 degrees)
|No rotation (cancels all previous rotations)
The options are cumulative i.e. rotating the page Clockwise once then rotating Clockwise a second time is the equivalent of clicking once on Upsidedown.
This does not change the orientation of the page in the file. You may, however, export the file in the orientation shown to any format other than Subset. If a PCL file is exported or saved as a Subset, the rotation is not preserved.
If you would like documents to be opened in a rotated state, use the Viewing page of the 'Options | Configuration...' dialog. See Configuring the view.